The present invention relates to an apparatus for use in adsorption and desorption based sorption heat pump processes. Sorption heat pump processes typically employ some adsorbent disposed in a metal vessel and on a metal screen or surface which provides support for the adsorbent and permits the adsorbent to be placed in contact with the fluid stream containing the adsorbable component over the range of conditions necessary for the adsorption and desorption. The metal structures and physical arrangement of these devices has placed certain process limitations which restrict the amount of adsorbent which actually comes in contact with the fluid stream, or is accompanied by heat transfer inefficiencies inherent in the disposition of the adsorbent.
In the operation of sorption heat pump systems, generally there are two or more solid beds containing a solid adsorbent. The solid adsorbent beds desorb refrigerant when heated and adsorb refrigerant vapor when cooled. In this manner the beds can be used to drive the refrigerant around a heat pump system to heat or cool another fluid such as a process stream or to provide space heating or cooling. In the heat pump system, commonly referred to as the heat pump loop, or a sorption refrigeration circuit, the refrigerant is desorbed from a first bed as it is heated to drive the refrigerant out of the first bed and the refrigerant vapor is conveyed to a condenser. In the condenser, the refrigerant vapor is cooled and condensed. The refrigerant condensate is then expanded to a lower pressure through an expansion valve and the low pressure condensate passes to an evaporator where the low pressure condensate is heat exchanged with the process stream or space to be conditioned to revaporize the condensate. When further heating no longer produces desorbed refrigerant from the first bed, the first bed is isolated and allowed to return to the adsorption conditions. When the adsorption conditions are established in the first bed, the refrigerant vapor from the evaporator is reintroduced to the first bed to complete the cycle. Generally two or more solid adsorbent beds are employed in a typical cycle wherein one bed is heated during the desorption stroke and the other bed is cooled during the adsorption stroke. The time for the completion of a full cycle of adsorption and desorption is known as the “cycle time.” The upper and lower temperatures will vary depending upon the selection of the refrigerant fluid and the adsorbent. Some thermodynamic processes for cooling and heating by adsorption of a refrigerating fluid on a solid adsorbent use zeolite and other sorption materials such as activated carbon and silica gel. U.S. Pat. No. 4,138,850 relates to a system for solar heat utilization employing a solid zeolite adsorbent mixed with a binder, pressed, and sintered into divider panels and hermetically sealed in containers. U.S. Pat. No. 4,637,218 relates to a heat pump system using zeolites as the solid adsorbent and water as the refrigerant wherein the zeolite is sliced into bricks or pressed into a desired configuration to establish a hermetically sealed space and thereby set up the propagation of a temperature front, or thermal wave through the adsorbent bed. U.S. Pat. No. 5,477,705 discloses an apparatus for refrigeration employing a compartmentalized reactor and alternate circulation of hot and cold fluids to create a thermal wave which passes through the compartments containing a solid adsorbent to desorb and adsorb a refrigerant. U.S. Pat. No. 4,548,046 relates to an apparatus for cooling or heating by adsorption of a refrigerating fluid on a solid adsorbent. The operations employ a plurality of tubes provided with parallel radial fins, the spaces between which are filled or covered with solid adsorbent such as Zeolite 13X located on the outside of the tubes. U.S. Pat. No. 5,518,977, which is hereby incorporated by reference, relates to sorption cooling devices which employ adsorbent coated surfaces to obtain a high cooling coefficient of performance.
U.S. Pat. No. 5,585,145 discloses a method for providing an adsorbent coating on a heat exchanger which comprises applying a flowable emulsion including a binder agent, water and a solid adsorbent material to the surface of the heat exchanger. The disclosure states that the binder can be an adhesive and that the thickness of the adsorbent coating can be dipped, painted or sprayed with a drying step comprising heating the layer at temperatures greater than 150° C. in order to obtain a durable adsorbent coating structure.
Many sorption chillers are designed with beads or extrudate as an adsorbent. In the present invention, as in U.S. Pat. No. 6,102,107, there are no beads or extrudates with their resistance to heat transfer, but instead there is a compact heat exchanger module that comprises a laminate of adsorbent, especially zeolite, in a polymeric or polymeric fiber matrix. This laminate is on a substrate that can support the laminate and can be employed in the hot and wet environment of the adsorber/generator.
U.S. Pat. No. 6,102,107, incorporated herein in its entirety, teaches the use of a plate-fin-tube arrangement employing a laminate composed of thin polymeric fiber matrix on a metallic fin structure. Conventional tubing is laced through the fins by punching holes in the fin structure and forming collars of the fin metal that are maintained in intimate thermal contact with the tube surfaces. While this patent provided for greatly increased heat transfer and was a significant advance in the design and performance of adsorber/generators in sorption based heat pumps, it failed to deal with the problem of maximizing heat transfer when materials other than high thermal conductivity fin plates are used.
In addition to the problem of heat transfer resistance in some materials, a second potential problem arises when clean, uncoated aluminum is exposed to water vapor under vacuum conditions. This is the problem of corrosion of the aluminum surface and formation of AlOH radicals on the surface. This reaction liberates hydrogen gas and is a cause for the loss of vacuum under some conditions that may be present in the adsorber/generator of a sorption cooler or heat pump. Stainless steel could be used to solve this deficiency, but the low conductivity of stainless steel changes the heat transfer resistance. This makes adsorber/generators made from stainless steel incapable of transferring the required heat and can result in structures that are much more costly and only slightly more efficient than packed bed systems. One feature of the present invention is to allow for the use of aluminum with its superior heat transfer properties but without the corrosion problems of the prior art heat exchangers.
It is an object of the instant invention to provide an improved compact heat exchanger with the adsorbent matrix bonded directly to the plates. It is a further object of the invention to enable the application of a thin uniform layer of adsorbent material which is intimately bonded to a heat transfer surface. Another object of the present invention is to enable a rapid heating and cooling cycle with the purpose of achieving a high specific power and a high coefficient of performance for the sorption cooling cycle. Yet another object of the present invention is to provide a heat exchanger geometry that is effective regardless of the heat conductivity of the fin material that is chosen.